Vulcanization of caoutchouc



Patented n... 4, 1927.

CLAYTON W. JB EDFORD, OF AKRON,

OHIO, ASSIGNOR TO THE B. IE. GOODRICH COMPANY,

OF NEW YORK, N. Y.', A CORPORATION OF .NEW- YORK, AND THE GOODYEAR TIRE AND RUBBER COMPANY, OF AKRON, OHIO, A CORPORATION OF OHIO.

VULCANIZATION or oAoU'rcHoUc.

No Drawing. Application filed December 28, 1923, Serial No. 683,233. Renewed June 5, 1926.

This invention relates to the art of vulcanizing rubber by the aid of a vulcanization accelerator and its chief object is to provide an improved method of vulcanizing rubber wherebypremature vulcanization or scorching of the rubber compound, such as often results from incorporating powerful or-low temperature accelerators with the rubber on the mixing mill, may be conveniently avoided without sacrificing curing power of the accelerator.

Zinc dithiocarba'mates and zinc mcrcaptides are known to the art as powerful accelerators of vulcanization. They are characterized by rapid curing power even at ordinary temperatures and much trouble is experienced with scorching or outing on the mills or calenders. These difficulties are avoided to a certain extent by the use of low temperatures during processing, use vof low sulfur content or low accelerator content in the rubber mix or by such methods as mixing the sulfur and accelerator into separate portions of rubber, such master batches being mixed just before use or built up 'in alternate calendered plies. These methods diminish the production from a given equipment of mills and calenders, decrease the output of a given equipment of curing apparatus, or necessitate greatly increased labor costs.

Disulfides, such as tetramethyl thiuram disulfide or mercaptobenzothiazol disulfide, are also known to the art as powerful accelerators but are characterized as functioning at substantially higher temperatures than the corresponding zinc salts. Being therefore comparatively free from scorching and-air curing they are in many instances preferred to the zinc dithiocarbamates and zinc mercaptides even though they show a lower degree of acceleration.

According to the inventions, disclosed in this and my copending divisional application Serial No.-8,543, I have provided a method of transforming the disulfides into the corresponding. zinc salts, with the resultant increase in acceleration, after the indisulfides into the rubcorporation of such ber mix and subsequent to all factory ma nipulations wherein scorching or air curing are undesirable. This process is accomplished by mixing and calendering or otherwise manipulating a mixture of rubber, me-

tallic oxide, sulfur, disulfide and other com- Example 1.

A rubber mix is prepared according to the formula: rubber-100, sulfur-4, zinc oxide-5, tetramethyl thiuram disulfidc 0.25. This stock will not cure at ordinary temperatures in three months, but after treatment with ammonia gas until saturated and then exposed to the atmosphere, aircuring takes place in about one week. Before treatment with ammonia the stock will not cure in hot air in minutes at 80 C.,

while after treatment an overcurc is ob tamed under the same conditions.

A similar increase in curing power is found by the use of dimethylamine vapors or by painting the cold stock with tributylamine or aniline.

I also find that hydrogensulfidc and like, substances have the power of changing the disulfides to dithiocarbamic acids or mcrcap- 'poundin g ingredients, if desired, to form the tans, whereby zinc salts are formed in the presence of zinc oxide. Such materials may be usedin the place of amine or ammonia in Example 1, with the precaution that excess of such gases be avoided as their ultimate action is to change all the metallic oxide in the rubber mix to metallic sulfides and it is well known that without the pres ence of soluble forms of the metal, the dithiocarbamic acids or mercaptans have very low accelerating action.

I find two principal advantages in the use of amines or ammonia over the similar used hydrogensulfide' or the like: 1. An excess of the amine or ammonia is not detrimental and there is therefore no danger of exposing the rubber mix to their action for too long a tim 2. The zinc dithiocarbamates or zine tion is partially or mercaptides asformed from the disulfides by the action of ammonia or amines in the presence of zinc'oxlde have the power of combining with still further quantitiesof example.

Example 2.

A rubber mix is prepared according to the formula: rubber-J00, Slllflll'4:, zinc oxide5, zinc dimethyl dithiocarbamateO.25. The mix is divided into two parts, one (a) being left untreated, whilethe other (6) is exposed to ammonia gas until saturated and then allowed to stand in air until all odor of ammonia is lost. Portion (b) will air cure at ordinary temperatures in one week, while (a) will start to air cure in about three weeks. Portion will cure in a hot air oven in twenty-five minutes at 80 'C., while (a) will still be undercured. V

Ifthe mix described in Example N o. 2, be treated with hydrogen sulfide the accelerawholly destroyed for low 1 temperature curing, which illustrates'the action of an excess of fur, accelerator and hydrogen sulfide on the disulfides in Example No. 1. i

The action of hydrogensulfide, ammonia,

amines or the like on mixes of rubber, sulmetallic oxides is not limited to the dry mixture, as is shown by the following data.

Example 3.

A mix comprising, rubber-100, zinc oxide-"+5, sulfur-43 and tetramethyl-thiurarfidisulfidel (parts by weight) is'made into a cement by employing benzene as the solvent. Thiscement, it treated with ammonia gas for twenty seconds will gel or air cure in 13 days or if treated with hydrogen sulfide forthirty seconds will gel in .24 hours. Extending thetime of ammonia treatment increases the rate of cure while excess of hydrogen sulfide will entirely prevent gelation. The untreated cement will stand fol-several months without vulcanization.

I do not limit myself to any definite set of conditions during the exposure of the rubber mix to such gases, vapors or liquids as change the disulfidbs to dithiocarbai'nic acids or mercaptans. I may .apply a liquid directly to the her mix and allow .the same to penetrate the stock, or I may apply pressure during treatment with gases or vapors. After such treatment I may allow vulcanization to take place at room temperature, or I may speed the cur- 'ing process .by vulcanizing in hot air or' steam, with or without molds, or by other suitable procedure.

I claim: v 1. A method of effecting the vulcanization zinc salt surface of the rubfinal shape, treating the mix of a rubber mix that comprises mixing therein an organic disulfide having a double bond adjacent to the group CS'SC, treating the mix with hydrogen sulfide to produce the grouping CSH and vulcanizing the product.

2. A method of effecting the vulcanization of a rubber mix that comprises mixing therein a metallic oxide and an organic disulfide having a double bond adjacent to the group C-S.-SC, treating the mix with hydrogen sulfide. to produce a metallic salt of the acidic group CSH, and vulcanizing the product.

3. A method of efi'ecting'the vulcanizatherein zincoxide and an organic disulfide having a double bond adjacent to the group CSSC, treating themix with hydrogen sulfide to produce a zinc salt of the acidic group C-SH, and vulcanizing the product.

4. A method of effecting the vulcanization of a rubber mix that comprises mixing therein zinc oxide and a thiuramdisulfide, treating the mix with hydrogen sulfide to react with the zinc oxide and the thiuramdisulfide to produce a zinc salt of a dithiocarbamic acid, and vulcanizing the product.

5. A method of effecting the vulcanization of a rubber mix that comprises mixing therein zinc oxide and tetramethylthiuramdisulfide, sulfide to react with the zinc oxide and the tetramethylthiuramdisulfide to produce the of dimethyldithiocarbamic acid, and vulcanizing the product.

6. A method of efllecting the vulcanization of a rubber mix that comprises mixing therein an organic disulfide having a double bond adjacent to the group CSSC, forming the-unvulcanized mix into substantially its with hydrogen sulfide to produce the grouping vulcanizing the product. I

7. A method of effecting the vulcanization of rubber that comprises admixing rubber with sulfur, a metallic oxide and a thiuramdisulfide, forming the unvulcanized mix into substantially its final shape, associating therewith hydrogen sulfide to produce from the disulfide and the metallic oxide a me tallic salt of a dithiocarbamic acid,.and vul; canizing the product.

8. A method of eflecting the vulcaniza comprises admlxlng ruba dithiocarbamic acid, aiid'vulcanizing the product.

.9. A method 4 of eifecting the vulcanization of rubber that comprises admixing rub- CSH and treating the mix with hydrogen her with sulfur, a metallic oxide and tetramethylthiuramdisulfide, forming the unvulcanized mix into substantially its final shape, associating therewith hydrogen sulfide to produce zinc dimethyldithiocarbamatefrom the disulfide and the zinc oxide, and vulcanizing the product.

10. A method of effecting the vulcanization of a rubber mix that comprises incorporating therein an organic disulfide having a double bond adjacent the grouping CS-SC, forming a cement of the mixture, and treating the cement with hydrogen sulfide to react with the disulfide to produce the grouping CSH and vulcanizing the product.

11. A method of effecting the vulcanization of rubber that comprises admixing a I vulcanizing agent with rubber, associatin an accelerator consisting of a comminute" material therewith and treating the resulting product with hydrogen sulfide to activate the accelerator.

12. A vulcanized'rubber product composed of a rubber compound admixed with a metallic oxide and an organic disulfide having a double bond adjacent to the group C-S- SC and treated with hydrogen sulfide to produce from the disulfide and the metallic oxide a metallic salt of the group CSH. In witness whereof, I have hereunto signed my name. a I

CLAYTON W. BEDFORD. 

